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| Questão | Responda |
| What is the principle of Conservation of Energy? | That "Energy can not be created or destroyed". |
| A ride is fired into the sky by rubber bands of a catapult. Explain the changes to the energy stores as the ride moves upwards. | 1. It's elastic potential energy is increased, due to the stretch of rubber bands. 2. Kinetic energy increases due to fast movement of ride. 3. Gravitational potential increases due to height off ground. |
| Work done, (J) = (Work is done on the object by the force) | Force Applied x Distance moved (Newtons,N) (metres, m) |
| Calculate the work done when a force of 20N makes an object move 4.8m in the direction of force. | Force x Distance. 20N x 4.8m = 96J |
| Change in G.P.E (J) = | weight, (N) x change in height (m) OR mass (kg) x g.f.s (N/kg) x change in height (m) |
| Kinetic Energy (J) = | 1/2 x Mass (kg) x Speed² (m/s²) |
| elastic potential energy (J) = | 1/2 x spring constant (N/m) x extension² (m²) |
| A car moving at a constant speed has 360,000J in its kinetic energy store. When brakes are applied, it stops in 100m. Calculate the force that stops the car. | Work done ÷ Distance moved. 360,000J ÷ 100m = 3,600N |
| Calculate the kinetic energy stored in a vehicle of mass 500kg moving at a speed of 12m/s. | Kinetic energy= 1/2 m v² 0.5 x 500kg x (12m/s)² = 36,000J |
| Wasted energy = | Energy that is not usefully transferred. Eventually transferred to the surroundings which become warmer. |
| Efficiency = | Useful output energy transferred ÷ total input energy supplied. |
| Examples of improving Efficiency: | - Lubricate moving parts to reduce friction. - Cut out noise, reduce vibration. - in circuits, use wires with little resistance. |
| Power (W) = | energy transferred (J) ÷ time taken (s) |
| power wasted = | total power in - useful power out. |
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